Michigan Gov. Rick Snyder today vetoed a bill that would have allowed concealed guns in public schools, just four days after a man broke into a Connecticut elementary school and shot 20 pupils to death.

The 54-year-old Republican killed the measure, approved by Michigan's Legislature less than 24 hours before the Newtown killings, primarily because it didn't allow day-care centers, hospitals and other public entities to opt out, according to a letter sent to the state Senate.

“While we must vigilantly protect the rights of law-abiding firearm owners, we also must ensure the right of designated public entities to exercise their best discretion,” Snyder said in a statement. “These public venues need clear legal authority to ban firearms.”

The measure was among several still under consideration in states, including Ohio, Oklahoma and Alabama, to redefine where residents may carry or keep guns. The Dec. 14 Newtown rampage by 20-year-old Adam Lanza, who used a semiautomatic rifle to kill 27, including his mother and himself, caused Snyder to take a closer look at the legislation, according to the statement.

Hospital and school groups and a coalition of clergy opposed the Michigan bill. Under the legislation, retired police officers and those with permits who have had additional training would have been allowed to take concealed guns into the zones.

Republican House Speaker Jase Bolger of Marshall said that despite the veto, people can continue to openly arm themselves in schools, churches and other public areas.

“Neither the governor's approval nor his veto will stop evil from preying on innocent people,” Bolger said in an emailed statement. “We know that criminals do not respect gun-free zones.”

Only one Senate Democrat voted for the measure, said Bob McCann, a spokesman for the caucus. He said the Connecticut shootings should prompt debate over violence, guns and mental health care.

That debate is happening in states across the country.

Like Snyder, Ohio Gov. John Kasich has faced pressure to reject legislation expanding where owners can bring their guns. In his case, it would be right beneath him: House Bill 495 would allow firearms in parking garages under the Statehouse in Columbus.

“I'm a Second Amendment supporter, and that's not going to change,” he said in a statement.

Oklahoma Republican Rep. Mark McCullough of Sapulpa said he'd push a bill allowing teachers and administrators to carry weapons, according to The Associated Press.

South Dakota Republican Betty Olson of Prairie City plans to introduce a similar measure next month, the AP said.

In the past two years, 19 states have considered expansions of gun rights in workplaces, colleges and government property, according to the Law Center to Prevent Gun Violence in San Francisco. Lawmakers in Tennessee, Alabama, South Carolina and Pennsylvania are pushing legislation that would create a right for workers to keep guns in cars parked at work, with or without employers' consent.

Texas Governor Rick Perry said Monday that people with concealed-carry permits should be able to take firearms anywhere. He spoke at an event in North Richland Hills hosted by the Northeast Tarrant Tea Party.

The Connecticut killings prompted some Democratic leaders to come out in support of further restrictions.

Gov. Andrew Cuomo of New York and Gov. Dannel Malloy of Connecticut, who broke down in tears when recalling how he informed parents that their children had been killed, indicated their support Monday for measures such as bans on high-capacity ammunition magazines like those used in Newtown.

The day before the Connecticut shootings, Colorado John Hickenlooper told The Associated Press that “the time is right” to consider gun-control laws. Today, the governor, whose fellow Democrats control the Legislature, introduced an $18.5-million plan to redesign the state's mental-health system, making records more easily available for gun-purchase background checks, his office said in a statement.

His state has been the site of two high-profile mass killings. In July, a masked gunman opened fire at a midnight movie in Aurora, killing 12 and injuring 58. In 1999, two students shot 12 classmates and a teacher at Columbine High School before killing themselves.

In California, Democratic Sens. Kevin de Leon of Los Angeles and Leland Yee of San Francisco said they would introduce measures to make it harder to get certain ammunition and to strengthen an assault-weapon ban.

California prohibits semiautomatic assault weapons, including the Bushmaster used by the killer in Connecticut, and magazines that can hold more than 10 rounds of ammunition, according to the attorney general's website. Gov. Jerry Brown's office didn't respond to a request for comment on whether he'd support such measures.

President Barack Obama, at a prayer vigil for the victims, pledged Dec. 16 to use “whatever power” he holds to prevent similar killings.

Michigan state Sen. Rick Jones, a Republican, said in an interview today that politicians are powerless.

“We are terribly hurt by this horrific shooting in Connecticut, but there is no law that we can pass that would prevent it,” Jones said.